We have previous data suggesting that one of the mechanisms basic to olfactory discrimination may be the differential sorption of molecules of different odorants across the mucosa. We will pursue this line of study in frogs and dogs by radioisotopically defining exactly how the molecules are distributed to the receptors, what parameters affect these distributions, and how the distributions may make an impact upon the processing of olfactory information by the central nervous system. 1. We are developing a hot-wire anemometer to profile air movements into and out of the external nares of bullfrogs and dogs. We will develop an odorant delivery system to faithfully reproduce these normal odorant sampling air flows. 2. Using the anemometer profile we will present animals with tritium-labelled odorants, and using liquid scintillation counting to measure the resultant radioactivity in different mucosal regions, we will map exactly how the molecules of different odorants are distributed across the length and breadth of the olfactory receptor sheet. The stability of these distribution patterns will be tested as a function of stimulus duration, concentration and flow rate. 3. Using autoradiographs, we will follow the distribution of the molecules vertically through the depth of the mucosa, noting particularly any differential filtering of different chemicals. 4. By recording from single mitral cells in the olfactory bulb previously shown by electrical stimulation to receive their input from particular regions of the olfactory receptor sheet, we will determine whether the differential molecular distributions established across the mucosa are topographically represented by a group of mitral cells in the olfactory bulb. 5. To extend our approach to humans, we will, using computerized scintillation camera imagery, follow in cadaver noses the access of 133xenon-laden air to the olfactory cleft under a variety of artificially produced sniffing strategies. 6. A new departure will be to pursue psychophysically in humans the possibility of laterality in the olfactory system.